Heretofore, a technique, called “AWS (Accelerated Warm-up System)”, has been employed in a spark ignition engine to achieve rapid activation of a catalytic converter provided in an exhaust passage, in some cases. This AWS is a technique configured to, when the catalytic converter is in an un-activated state, for example, just after a cold start of the engine, increase an intake air amount as compared to when the catalytic converter is in an activated state under the same engine operation condition (e.g., under an idling operation), and retard an ignition timing beyond a top dead center of a compression stroke, to allow an air-fuel mixture to undergo after-burning in a subsequent expansion stroke to thereby increase an exhaust gas temperature and thus an exhaust gas heat amount to accelerate warmup of the catalytic converter (see, for example, the following Patent Literature 1).